Their lawn is Tall Fescue, I didn't take the sample but one of my guys did. I told him to sample 4-6" deep consistently. Any help on what to recommend applying & when is greatly appreciated.

Just a heads up that oftentimes P levels decrease significantly as you go deeper into the soil. See the attached graphic taken from a Wisconsin putting green. Courtesy Dr. Soldat UW-M. Most important thing is consistency of depth from sample to sample though and year to year to ensure results that are worth interpreting.